1. Technical Field
The present invention relates to a flat panel display apparatus, and more particularly, to a plasma display panel (PDP) including sustain electrodes having a double gap and a method of manufacturing the panel.
2. Related Art
A PDP is a display apparatus using a gas discharge. A PDP is more suitable to a large size display than other flat panel displays such as a liquid crystal display (LCD), a field emission display (FED), and an electroluminescent display (ELD).
A large size PDP can be manufactured because it has a structure, in which a front glass substrate having a discharge electrode is separated from a rear glass substrate having a fluorescent material by a micro gap of 0.1–0.2 mm and plasma is formed therebetween, so that it operates as long as the gap between the front and rear glass substrates is exactly maintained.
PDPs are divided into a direct current (DC) type and an alternating current (AC) type. In the DC type, an electrode is directly exposed to a discharge gas, so the electrode sputters and evaporates with discharge repetitions. The AC type overcomes these problems of the DC type. In order to prevent an electrode from evaporating during a discharge, the AC type includes a dielectric layer covering the electrode. In addition, in order to prevent a fluorescent material from being damaged by ions generated during a discharge, the AC type includes electrodes, which are arranged in a horizontal direction. When starting a discharge using these electrodes, ions generated during the discharge are prevented from being injected into the fluorescent material, and only ultraviolet rays generated during the discharge are radiated onto the fluorescent material.
FIG. 1 shows the structure of such an AC type PDP (hereinafter, referred to as a conventional PDP). Referring to FIG. 1, the conventional PDP includes a front glass substrate 10 and a rear glass substrate 12, which face each other in parallel. Transparent first and second sustain electrodes 14a and 14b are arranged in parallel on a side (hereinafter, referred to as a rear side) of the front glass substrate 10, which faces the rear glass substrate 12. As shown in FIG. 2, a gap “d” exists between the first and second sustain electrodes 14a and 14b. First and second bus electrodes 16a and 16b are disposed on the first and second sustain electrodes 14a and 14b, respectively, in parallel with the first and second sustain electrodes 14a and 14b, respectively. The first and second bus electrodes 16a and 16b prevent a drop in voltage caused by resistance during a discharge. The first and second sustain electrodes 14a and 14b and the first and second bus electrodes 16a and 16b are covered with a first dielectric layer 18. The first dielectric layer 18 is covered with a protective layer 20. The protective layer 20 protects the first dielectric layer 18 from a discharge so that the conventional PDP can reliably operate for a long period of time and emits a large amount of secondary electrons during the discharge, thereby lowering a discharge voltage. A magnesium oxide (MgO) layer is widely used as the protective layer 20.
A plurality of address electrodes 22 used for writing data are disposed on the rear glass substrate 12. The address electrodes 22 are arranged in parallel with one another and are perpendicular to the first and second sustain electrodes 14a and 14b. Three address electrodes 22 are provided for each pixel. In a single pixel, three address electrodes 22 correspond to a red fluorescent material, a green fluorescent material, and a blue fluorescent material, respectively. The address electrodes 22 are covered with a second dielectric layer 24. A plurality of barrier ribs are disposed on the second dielectric layer 24, which is provided for light reflection. The plurality of barrier ribs 26 are spaced apart by a predetermined gap and parallel with the address electrodes 22. Each barrier rib 26 is disposed on the second dielectric layer 24 between adjacent address electrodes 22. In other words, the address electrodes 22 are alternately arranged with the barrier ribs 26. The barrier ribs 26 become in close contact with the protective layer 20 provided on the rear side of the front glass substrate 10 when the front and rear glass substrates 10 and 12 are joined together. Fluorescent materials 28a, 28b, and 28c are deposited in gaps between the barrier ribs 26 and excited by ultraviolet rays. The first fluorescent material 28a emits red (R) light, the second fluorescent material 28b emits green (G) light, and the third fluorescent material 28c emits blue (B) light.
After sealing the front glass substrate 10 to the rear glass substrate 12, unnecessary gas is evacuated from a gap therebetween, and then a plasma forming gas is injected into the gap. Although a single gas (for example, neon (Ne)) can be used as the plasma forming gas, a mixed gas (for example, Ne+Xe) is widely used.
In this conventional PDP, a pressure of the plasma forming gas (a partial pressure of a particular gas in a case of a mixed gas) needs to be maintained at a high level in order to avoid an increase in a sputter rate (SR) on the surface of the protective layer 20, and thus a high discharge voltage is required.
More specifically, referring to paschen curves G1 and G2 shown in FIG. 3, a discharge voltage can be lowered by adjusting a pressure P of a plasma forming gas and a gap “d” between the first and second sustain electrodes 14a and 14b such that a product Pd of the pressure P and the gap “d” is 1. For example, when the gap “d” is 100 μm (i.e., 0.01 cm), if the pressure P is maintained at 100 torr, a discharge voltage of a PDP can be lowered.
However, when the pressure P of a plasma forming gas is lowered, an SR on the surface of the protective layer 20 rapidly increases according to Formula (1), which defines the SR.SR=(j/P)2.5  (1)
Where, “j” is an electric current density of the surfaces of the sustain electrodes 14a and 14b. 
For this reason, in the conventional PDP, the pressures of a plasma forming gas must be maintained at a high level (e.g., 300–500 torr), and thus a discharge voltage is also high.